Separation and recovery of uranium from uranium-aluminum alloys



United States Patent 3,201,191 SEPARATION AND RECOVERY OF FRO URANIUM-ALUMINUM ALLoYs Herman S. Gile, Richland, Wash.,' assignor to the United States of America as represented hythe United States Atomic Energy Commission No Drawing. Filed Mar. 12, 1952, Ser. No. 276,227

6- Claims. (Cl: 23-145) This invention deals with the separation and recovery of uranium from uranium-aluminum alloys.

Uranium-aluminum alloys in the form of rods or slugs are used, for instance, in some neutronic reactors and the recovery of uranium from'these alloys becomes necessary in various instances. In the first place, the uranium is to be isolated and recovered after the slugs have been subjected to irradiation or neutron bombardment so that the uranium may then be re-used; this is particularly im-v portant, since these slugs usually are enriched in U wln'ch is very valuable so that 'a practically complete recovery is of great importance. Another instance when the recovery of uranium in such slugs is desirable is when, before irradiation, it has been found that the slugs have flaws so that they are not suitable for use in a neutronic reactor. Also in this case, the ingredients of the alloy, and in particular the uranium, are to be recovered. The process of this invention is applicable to any uranium-aluminum alloy, for instance, also to alloys containing a relatively low percentage of uranium as they are used as construction materials on account of their high strength and toughness.

The most desirable methods of separating uranium from uranium-aluminum alloys comprise dissolving the alloys, for instance, in a mixture of sodium nitrate and sodium hydroxide solutions; the dissolving step usually makes mechanical disintegration of the slugs or other metal pieces prior to chemical processing unnecessary. It is most desirable in such dissolving processes to obtain a comparatively rapid dissolution, particularly when the uranium of the alloy is enriched in U the critical mass of U is relatively low, and small dissolvers, and con sequently a great number of dissolvers, have therefore to be used. A short dissolution time, however, reduces the number of such small dissolvers required.

When using a sodium hydroxide-sodium nitrate solution for the uranium recovery of uranium-aluminum slugs, the aluminum is dissolved as the aluminate and uranium precipitated in the form of oxides. It was found rather diflicult to adjust the quantities of sodium hydroxide and nitrate to optimal conditions. For instance, a relatively high sodium hydroxide concentration was found to be advantageous in bringing about dissolution within a relatively short period of time, while on the other hand increase of sodium hydroxide concentration resulted in higher uranium losses during separation of the precipitated uranium oxide from the aluminate solution.

The effect of a number of flocculants on the uranium loss was studied. The flocculants were added to the aluminate-uranium oxide precipitate mixture prior to separation by centrifugation or filtration. However, none of the flocculants added was found to improve the uranium recovery.

It was discovered, though, that the addition of barium nitrate to the aluminate-uranium oxide precipitate mixture considerably reduced the loss of uranium.

Table I Additions Exper' ent MNaOH/ M NaNOg/ U Loss, No. M Al M Al Percent Agent M 1 1. 25 1. 0 0. 062 2 1. 25 1. O Ba 0. 02 0. 041

These experiments show that the addition of barium nitrate lowers the uranium loss from 0.062 to 0.041%.

As has already been mentioned, it is very difiicult to select optimal conditions for the sodium hydroxide-sodium nitrate dissolver solution with regard to both, minimum uranium loss and minimum dissolving time; this is also the case when barium nitrate was added prior to separation of the precipitated uranium oxides For instance, a molal ratio of 121.521 for sodium hydroxide: sodium nitratezaluminum, when employed for a slug 1%" in diameter and containing 7.5% uranium, required six hours for dissolution; however, separation from the aluminum after the addition of barium nitrate so as to obtain a concentration of 0.02 M, was not complete because part of it precipitated with the uranium as aluminum hydroxide. The uranium loss in this instance was very small; it amounted to 0.03%

In another similar experiment, the ratio was varied so that the sodium hydroxide was the predominant ingredient of the solvent. The ratio of sodium hydroxidezsodium nitratezaluminum amounted to 1.75:0.5:1. This solvent mixture dissolved a slug of the same type in four hours and did not cause any precipitation of aluminum hydroxide. However, the uranium loss, determined after addition of barium nitrate and centrifugation, was considerably greater and amounted to from 0.1 to 0.2%.

However, it was now found that, when sodium nitrite was present in a sodium hydroxide-sodium nitrate dissolver solution, preferably in one containing at least 1.5 moles of sodium hydroxide per 1 mole of aluminum, and barium nitrate was then added prior to the removal of the uranium oxides, the uranium loss was reduced without a decrease of the dissolving rate. The process of this invention is based on this finding.

It is an object of this invention to provide a process for the separation of uranium from uranium-aluminum alloys by selective dissolution in which the losses of uranium are kept relatively low, and at the same time a relatively short dissolution time is required.

It is another object of this invention to provide a process for the recovery of uranium from uranium-aluminum alloys by means of dissolution in sodium hydroxide-sodium nitrate whereby a relatively stable solution of aluminate is formed in which no gel formation and/or aluminum hydroxide precipitation take place.

These objects are accomplished by using a sodium hydroxide-sodium nitrate-sodium nitrite solution for dissolving the uranium-aluminum alloy, then adding barium nitrate to the mixture obtained, and finally separating the alkali aluminate-containing solution from the uranium oxide-containing residue.

A molal ratio for sodium hydroxide:sodium nitrate: sodium nitritezaluminum of 12:0.252:0.11:1 was found suitable, the ratio of 1.5 :0.5 20.5:1, however, being preferred. With this preferred solution, complete dissolution of a slug described above was accomplished in about four hours. Filtration or centrifugation, after making the solution 0.02 M in barium nitrate, brought about a separation with a loss of uranium of as low as 0.028%.

In the following Table II, the results of some experiments carried out with varying quantities of the components of the solvent, with or without the addition of sodium nitrite, are compiled. In all instances, barium nitrate was added in a quantity to obtain a concentration of 0.02 M before separation of the uranium oxides from the aluminate. While the separation was carried out by centrifugation in tests 1, 2, 3 and 7, filtration was applied in experiments 4, 5 and 6. It is obvious from this table that when nitrite was added, both the dissolution time and the uranium loss had minimum values, while without nitrite, either one was relatively high depending on the solvent used.

The barium nitrate concentration may vary widely; however, a concentration of 0.02 M was always found satisfactory.

It is advantageous to carry out the dissolv ng step at elevated temperature, and best results were obtained by heating the solution to the boiling point and replacing from time to time the water evaporated in order to maintain the volume constant.

The filtration residue, after separation, may be washed with 0.5 M sodium hydroxide solution saturated with barium nitrate whereby about 99% of the aluminate adhering to the residue is removed without increasing the uranium-loss by more than about 0.01%.

It will be understood that this invention is not to be limited to the details given herein but that it may be modified within the scope of the appended claims.

What is claimed is:

1. A process for separating uranium from aluminum contained in uranium-aluminum alloys, comprising react ing said alloys with an aqueous solution of alkali metal hydroxide, alkali metal nitrate and alkali metal nitrite, adding barium nitrate to the solution formed, and separating an alkali alurninate-containing solution from a uranium oxide-containing residue.

2. The process of claim 1 wherein the molal ratio of alkali metal hydroxidez-alkali metal nitratezalkali metal nitrite: aluminum is 12:0.252:0.1-1:1.

3. The process of claim 2 wherein the ratio is 1.5:O.5:0.5:1.

4. The process of claim 1 wherein the barium nitrate is present in a concentration of 0.02 M.

5. The process of claim 1 wherein the alloy is reacted with said solution at elevated temperature.

6. The process of claim 1 wherein the separated uranium oxide residue is washed with 0.5 M sodium hydroxide solution saturated with barium nitrate for removal of adhering aluminate.

No references cited.

CARL D. QUARFORTH, Primary Examiner.

WILLIAM G. WILES, Examiner. 

1. A PROCESS FOR SEPARATING URANIUM FROM ALUMINUM CONTAINED IN URANIUM-ALUMINUM ALLOYS, COMPRISING REACTING SAID ALLOYS WITH AN AQUEOUS SOLUTION OF ALKALI METAL HYDROXIDE, ALKALI METAL NITRATE AND ALKALI METAL NITRITE, ADDING BARIUM NITRATE TO THE SOLUTION FORMED, AND SEPARATING AN ALKALI ALUMINATE-CONTAINING SOLUTION FROM A URANIUM OXIDE-CONTAINING RESIDUE. 